1. Field of the Invention
The present invention relates to a file reproducing apparatus and a file reproducing method for reproducing motion picture files recorded on a recording medium by using a FAT file system.
2. Related Art
In recent years, mobile data processing apparatuses such as digital still cameras have come to be provided with the function of recording and reproducing motion pictures in addition to still pictures. For the recording of still and motion pictures, most of these data processing apparatuses adopt a recording medium which is a semiconductor memory-equipped detachable card. The recording of data onto such a recording medium is managed file by file by the FAT (File Allocation Table) file system of disk operating system (hereinafter referred to as DOS).
With increasingly greater capacities of recent recording media, there is a trend that the recording time of motion pictures is becoming longer. The increased recording time of motion pictures requires the double-speed reproducing function such as fast forward and rewind during reproduction so as to retrieve desired scenes as soon as possible. The double-speed reproduction in a motion picture file is usually achieved by skipping the video frames of the motion picture file at a constant interval. A motion picture file is recorded on a recording medium in units of clusters. The clusters in which file data are stored are not necessarily recorded in order of increasing or decreasing cluster numbers because of properties of the FAT file system. Therefore, the position of the video frame to be reproduced is retrieved based on the information of the cluster number indicated on the file allocation table (hereinafter referred to as FAT).
The retrieving operation of a file with the use of the FAT will be described as follows with reference to FIG. 12. A recording medium generally contains directory information 203a and FAT 202a as file management information. In the FAT 202a, at a position corresponding to a cluster number of one cluster, a cluster number of the other cluster which follows the one cluster is recorded.
When a motion picture file is reproduced, the directory information 203a is first referred to, and then the leading cluster number of the motion picture file is acquired based on the file name of the motion picture file. Then, data in the cluster (cluster 2 in FIG. 12) of the leading cluster number in the data region 204 of the recording medium is read and reproduced. After this, FAT 202a is referred to and the cluster number of the cluster to be reproduced next (cluster 3 in FIG. 12) is acquired so as to read and reproduce data from the data region 204. Hereafter, the cluster numbers of the clusters to be reproduced next are acquired in sequence while referring to FAT 202a until the value of the FAT 202a reaches “0xFFFF” which indicates the end of the file. By specifying clusters one by one in this manner, the entire file is being read out.
However, the conventional FAT shown in FIG. 12 can be read only in the forward direction from the head of a file towards the end, and has problems in reading data in the reverse direction. More specifically, to specify one cluster immediately before the other cluster, it needs to read the FAT from the head in sequence to specify the cluster number of the one cluster when the other cluster appears. This takes a lot of time to specify the cluster number, making it impossible to read data smoothly in the reverse direction. The prior art disclosed in Japanese Patent Laid-open Publication No. 2001-338484 has solved this problem.
In the prior art, as shown in FIG. 13, the FAT is provided with a first storage area storing, at a position corresponding to a cluster number of one cluster, a cluster number of a cluster immediately following the one cluster and a second storage area storing, at the position, a cluster number of cluster immediately preceding the one cluster. This enables rapid reading in the reverse direction. For example, to retrieve a cluster number of cluster immediately before the cluster with a cluster number of “0x0008”, the second storage area with respect to a FAT entry corresponding to the cluster number of “0x0008” is referred. This allows a cluster number (“0x0004”) of a cluster immediately before the cluster having the cluster number of “0x0008” to be rapidly retrieved.
However, in the prior art, the FAT equipped with the second storage area is stored in the recording medium, which causes the problem of consuming the capacity of the recording medium. With an increase in the file size to be allocated by the FAT, the second storage area increases its capacity, thereby further consuming the capacity of the recording medium. This problem is particularly serious in the system using a recording medium with a small capacity (such as digital still cameras using a memory card).